I use checks for all my bills and for some co-pays. If I use it for co-pays, I always write it ahead of time except my signature.
I always paid with cash before, however for one of my doctors who switched practices I was double billed. Since I had shredded my statement and the receipt, I felt it was easier to just pay again. I don't drive so I couldn't go to my bank. This has happened twice.
Now I keep my receipt and also have a copy of the check for at least a year.
I do feel that people should fill them out ahead of time. Even when they go grocery shopping. It really bugs me when I get in the shortest line and the person in front of me decides they need to write a check and digs for the checkbook.
I love my ATM card!